The invention concerns a test gas leakage detection assembly.
A test gas leakage detection assembly having certain characteristics is known from DE-A-31 24 205. In a test gas leakage detector of that kind it is possible to perform a leakage detection process in two stages. As long as the pressure within the inlet area is still relatively high, the valve in the line leading to the intermediate connection remains closed. The gas mixture sucked in by the pre-vacuum pump arrives at the pre-vacuum side of the second stage of the friction pump. If there is test gas (helium, for example) already present in this gas owing to a relatively large leakage, it will then pass in a counter-flow through both stages of the friction pump into the detector and it is recorded. If the test sample does not have a large leakage, the valve in the line leading to the intermediate connection may be opened, so that the leakage detection process may be performed at a higher sensitivity.
In the described test gas leakage detector according to the state-of-the-art, the pre-vacuum pump is an oil-sealed pump so that there exists the danger of oil vapours entering the test sample connected at the inlet of the test gas leakage detector or the test chamber.